In the prior art, it is known that nail tips are glued onto the end of the natural fingernail with instant nail glue. A room temperature curing acrylic overlay is then brushed over the top in order to form a continuous ridge-covering film. An acrylic overlay essentially consists of an acrylic monomer which contains an accelerator, which is mixed with a peroxide catalyst dispersed in an acrylic polymer just prior to use, and thus sets into a hardened resin.
The use of room temperature curing acrylics to lengthen natural fingernails is well-known. See for example Lee and Orlowski U.S. Pat. No. 4,104,333 and Orlowski U.S. Pat. No. 4,495,172. Patents exist where the acrylic is brushed over a removable underlying form (Slack U.S. Pat. No. 2,799,282), as well as with different plastic co-extenders (Noskin U.S. Pat. No. 3,786,821 and Jarby U.S. Pat. No. 3,502,088). Similarly, the use of nail tips to lengthen nails is well known (see for example Matranga and Hokama U.S. Pat. No. 4,135,526). To those skilled in the art it has become common knowledge to apply acrylic resins over glues on nail tips as one convenient way to artificially lengthen nails. In spite of a large amount of commercial and scientific activity in this field one problem with the acrylic overlay persists. This is the problem of oxygen inhibition. The problem with the prior art just discussed is one of oxygen inhibition which- causes the top surface of the coated nail, that is, the overlay not to dry. More volatile, and thus more toxic monomers suffer less from this problem, but it is very desirable to refrain from the use of such materials with nail tips to avoid toxicity problems. The present invention concerns a solution to this dilemma. This background will not deal comprehensively with the body of work done in attempts to solve this problem, which is prevalent not only with acrylics but with other types of resins also. One solution that has been proposed, however, is central to this invention. That is the use of waxes to prevent the oxygen inhibition. The pertinent literature here is now discussed.
T. L. Phillips, British Plastics, February 1961, p. 69 "Polyester resins for coating applications" discloses a peroxide-initiated cure of a styrene/polyester mixture. This paper states that somewhere in the range of 0.001 to 3% by weight of a paraffin wax will eliminate the oxygen inhibition of surface curing. S. H. Schroeter and J. E. Moore in "The ultraviolet cure of solventless resins--pollution free method?", Nonpolluting Coatings and Coating Processes, J. L. Gordon and J. W. Prane, Eds., Plenum Publishing, New York, 1973, p. 135. Photoinitiation of resin cure is a well-known and common technique which is applied to acrylic and other resins in this paper. A variety of different waxes were found to have different degrees of effectiveness in stopping oxygen inhibition. These included Chlorowax, Naprowax, Acrawax, Epolene wax, carnauba wax, beeswax, ceresine wax, Oxazoline wax, stearic acid, stearyl methacrylate, methyl stearate, paraffin waxes and mineral oil. Of these the most effective, and materials of choice, were the straight-chain hydrocarbon paraffin waxes.
D. A. Bolon and K. K. Webb, J. App. Polymer Sci., Vol. 22, 2543-2551 (1978) "Barrier coats versus inert atmospheres. The elimination of oxygen inhibition in free-radical polymerizations." This discusses the effect of paraffin waxes of different melting points on the oxygen inhibition of different acrylics. They were effective in concentrations of around 1% by weight. Also the higher the temperature of the reaction, the higher the melting point of the wax that is needed. Nakao et al., Japan Kokai Tokyo Koho, 79 46,240 "Unsaturated polyester coating materials". Compositions contain a wax, polyester, and solvent to prevent oxygen inhibition. The only reason for mentioning this patent is that their use of the term "solvent" is totally different to the one used below in this disclosure. In this patent the term "solvent" refers to the reactive styrene moiety that is part of the polyester polymerization system, and the work is essentially no different from that of T. L. Phillips above.
Even with all the above elements already known we have found, as explained below, that the simple addition of wax to a standard acrylic nail extender did not satisfactorily prevent oxygen inhibition. Thus, it is not possible to make an acrylic overlay which could be brushed onto a natural nail, or a natural nail/nail tip combination as a relatively thin film that would dry to the necessarily completely dry surface, especially with the higher molecular weight and lower toxicity acrylic monomers as described in U.S. Pat. No. 4,104,333.
In addition to the oxygen inhibition problem there are two other disadvantages in the current art which this invention seeks to overcome. After the current formulations have hardened, they have a strong tendency to turn yellow. Also during application they are stiff and difficult to use and the subsequent coating is difficult to file and finish. The basic reason for this is in the recommended mode of application. The liquid acrylic monomer, containing a room temperature accelerator, is mixed with an acrylic polymer containing benzoyl peroxide catalyst. The normally recommended mixing ratio is in the range of 1:1 to 1:2 parts by weight of liquid to powder. This excessive powder makes stiff, difficult to work with mixtures.
The compositions described below greatly minimize these disadvantages. According to the present invention, it has become possible to use much less powder, resulting in easier to brush mixtures with less benzoyl peroxide and consequently less yellowing of the final product.